Lattice dynamics of high-pressure hydrogenated austenitic stainless steels

The vibrational spectra of hydrogenated austenitic stainless steels AiSI 304 (Fe/Cr18/Ni10) and AISI 310 (Fe/Cr25/Ni20) were investigated by inelastic neutron scattering. Based on the results of previous neutron diffraction studies, the data have been analysed by model calculations. The peaks corresponding to the optical modes show a significant broadening because of the variation of vibrational energies from one hydrogen site to another in the alloys. At high hydrogen contents (hydrogen-to-metal atomic ratios H/Me approximate to 1) the peak profile is dominated by hydrogen-hydrogen interactions. Correspondingly, the optical peaks show a splitting into longitudinal and transverse modes for H/Me approximate to 1. A continuous lowering of the vibrational energies with increasing hydrogen content was observed for both steels, reflecting a weakening of the hydrogen-metal interactions with increasing hydrogen-metal atomic distance.